After mulling it a bit more (and receiving an off-list reply from Rex), I
think Jay is saying that the threaded portion is not loaded in shear (which
is normally a design requirement, threads should _never_ be loaded in
shear), thus the threads do not affect the shear strength.
The tensile strength of the entire bolt includes the threads and is directly
affected by them. Coarse threads have a smaller minor diameter, so for the
same material a fine thread bolt has a higher tensile strength. Perhaps Jay
is saying the shear strength can be estimated as 60% of the shank's tensile
strength.
As I said before, shear strength can only be an estimate, the measured value
depends a good deal on how you measure it. To see this, just compare a dull
pair of tin snips to a sharp pair.
Randall
> Not to beat this too far into the ground, but I would think that
> threads or their absence, or their profile, would change stress
> concentrations and so the shear strength. Maybe tensile and shear
> strengths change the same amount with these effects?
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